GENEVA  The World Health Organisation (WHO) on Tuesday launched a drive to raise awareness of the risk of cancer, particularly to smokers, posed by uranium occurring naturally in the environment.

Uranium in the form of radon radioactive gas is responsible for between 6 and 15 percent of all lung cancers and is the second most important cause of the disease after smoking.

"On a global level, tens of thousands of lung cancer deaths annually can be attributed to radon," the United Nations health agency said in a statement.

Radon emanates from the soil and is present worldwide, although in differing concentrations, and for most people the home is where they face the greatest potential danger.

Moderate exposure can increase the risk of lung cancer in a smoker by 25 times, the WHO said.

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"Radon is all around us," Mike Repacholi, coordinator of the WHO's radiation and environmental health unit, told reporters. "Radon in our homes is the main source of exposure," he added.

The concentration in a home depends not just on the amount in the underlying soil, but also in the ease with which it is able to enter a building through cracks and openings and the degree to which air circulates freely inside.

For this reason it more likely to be a problem in cold climates, where doors and windows are kept closed, than in warmer countries, the WHO said.

Norway, Sweden and Finland have registered cases of particularly high radon concentration within homes, it noted.

But the problem can be easily resolved by improving construction regulations and, for existing housing, by increasing under-floor ventilation and sealing cracks and gaps in floors, the Geneva-based organisation said.

As part of the campaign, the WHO will put together a global radon database and coordinate work on risk assessment and exposure guidelines for its 192 member states, it added.